package pta.test04;

import java.util.Scanner;

public class rabbitProblem {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int anInt = scanner.nextInt();
        int rabbitNumber = rabbitNum(anInt);
        System.out.println(rabbitNumber);
    }
    public static int rabbitNum(int num){
        if (num==1||num==2)
            return num;
        else
            return rabbitNum(num-1)+rabbitNum(num-2);

    }
}
